Fabrication of tunneling junction for nanopore dna sequencing

ABSTRACT

A mechanism is provided for forming a nanodevice. A reservoir is filled with a conductive fluid, and a membrane is formed to separate the reservoir in the nanodevice. The membrane includes an electrode layer having a tunneling junction formed therein. The membrane is formed to have a nanopore formed through one or more other layers of the membrane such that the nanopore is aligned with the tunneling junction of the electrode layer. The tunneling junction of the electrode layer is narrowed to a narrowed size by electroplating or electroless deposition. When a voltage is applied to the electrode layer, a tunneling current is generated by a base in the tunneling junction to be measured as a current signature for distinguishing the base. When an organic coating is formed on an inside surface of the tunneling junction, transient bonds are formed between the electrode layer and the base.

BACKGROUND

The present invention relates to nanodevices, and more specifically to atunneling junction and nanopore structure in a nanodevice.

Nanopore sequencing is a method for determining the order in whichnucleotides occur on a strand of Deoxyribonucleic acid (DNA). A nanoporeis a small hole on the order of several nanometers in internal diameter.The theory behind nanopore sequencing has to do with what occurs whenthe nanopore is immersed in a conducting fluid and an electric potential(voltage) is applied across the nanopore. Under these conditions, aslight electric current due to conduction of ions through the nanoporecan be measured, and the amount of current is very sensitive to the sizeand shape of the nanopore. If single bases or strands of DNA pass (orpart of the DNA molecule passes) through the nanopore, this can create achange in the magnitude of the current through the nanopore. Otherelectrical or optical sensors can also be put around the nanopore sothat DNA bases can be differentiated while the DNA passes through thenanopore.

DNA could be driven through the nanopore by using various methods. Forexample, an electric field might attract the DNA towards the nanopore,and it might eventually pass through it. The scale of the nanopore meansthat the DNA may be forced through the hole as a long string, one baseat a time, rather like thread through the eye of a needle.

BRIEF SUMMARY

According to an embodiment, a method of forming a nanodevice isprovided. The method includes filing a reservoir with a conductive fluidand forming a membrane to separate the reservoir in the nanodevice. Themembrane includes an electrode layer having a tunneling junction formedtherein. The method includes forming the membrane to have a nanoporeformed through one or more other layers of the membrane such that thenanopore is aligned with the tunneling junction of the electrode layer;and narrowing the tunneling junction of the electrode layer to anarrowed size by electroplating or electroless deposition. When avoltage is applied to the electrode layer, a tunneling current isgenerated by a base in the tunneling junction to be measured as acurrent signature for distinguishing the base. When an organic coatingis formed on an inside surface of the tunneling junction, transientbonds are formed between the electrode layer and the base.

According to an embodiment, a method of forming a nanodevice isprovided. The method includes filing a reservoir with a conductivefluid, and forming a membrane to separate the reservoir in thenanodevice. The membrane includes an electrode layer having a tunnelingjunction formed therein. The membrane is formed to have a nanoporeformed through one or more other layers of the membrane such that thenanopore is aligned with the tunneling junction of the electrode layer.The tunneling junction is formed in the electrode layer by: patterningthe electrode layer with two boxes connected by a metal strip of theelectrode layer, coating an electron beam resist on top of the electrodelayer, and opening a gap shaped window through the electron beam resistto make a portion of the metal strip visible through the gap shapedwindow of the electron beam resist. The tunneling junction is formed inthe electrode layer by: etching away the portion of the metal strip thatwas visible through the gap shaped window of the electron beam resist,and removing the electron beam resist resulting in the electrode layerhaving the tunneling junction where the portion of the metal strip wasetched away. When a voltage is applied to the electrode layer, atunneling current is generated by a base in the tunneling junction to bemeasured as a current signature for distinguishing the base. When anorganic coating is formed on an inside surface of the tunnelingjunction, transient bonds are formed between the electrode layer and thebase.

According to an embodiment, a method of forming a nanodevice isprovided. The method includes filing a reservoir with a conductivefluid, and forming a membrane to separate the reservoir in thenanodevice. The membrane includes an electrode layer having a tunnelingjunction formed therein. The method includes forming the membrane tohave a nanopore formed through one or more other layers of the membranesuch that the nanopore is aligned with the tunneling junction of theelectrode layer. The tunneling junction is formed in the electrode layerby: coating an electron beam resist on top of a substrate, opening afirst window having a first elongated extension, and opening a secondwindow having a second elongated extension in which a portion of theelectron beam resist separates the first elongated extension from thesecond elongated extension. The tunneling junction is formed in theelectrode layer by depositing metal of the electrode layer to cover theelectron beam resist, to cover the first window having the firstelongated extension, and to cover the second window having the secondelongated extension. The tunneling junction is formed in the electrodelayer by removing the metal having been in contact with the electronbeam resist so as to leave the electrode layer having the tunnelingjunction in a pattern of the first window having the first elongatedextension and in the pattern of the second window having the secondelongated extension. The tunneling junction is formed and located wherethe portion of the electron beam resist was removed. When a voltage isapplied to the electrode layer, a tunneling current is generated by abase in the tunneling junction to be measured as a current signature fordistinguishing the base. When an organic coating is formed on an insidesurface of the tunneling junction, transient bonds are formed betweenthe electrode layer and the base.

According to an embodiment, a method of forming a nanodevice isprovided. The method includes filing a reservoir with a conductivefluid, and forming a membrane to separate the reservoir in thenanodevice. The membrane includes an electrode layer having a tunnelingjunction formed therein. The tunneling junction is formed into theelectrode layer by a focused ion beam. The method includes forming themembrane to have a nanopore formed through one or more other layers ofthe membrane such that the nanopore is aligned with the tunnelingjunction of the electrode layer, and narrowing the tunneling junction ofthe electrode layer to a narrowed size by electroplating or electrolessdeposition. When a voltage is applied to the electrode layer, atunneling current is generated by a base in the tunneling junction to bemeasured as a current signature for distinguishing the base. When anorganic coating is formed on an inside surface of the tunnelingjunction, transient bonds are formed between the electrode layer and thebase.

Other systems, methods, apparatus, design structures, and/or computerprogram products according to embodiments will be or become apparent toone with skill in the art upon review of the following drawings anddetailed description. It is intended that all such additional systems,methods, apparatus, design structures, and/or computer program productsbe included within this description, be within the scope of theembodiments, and be protected by the accompanying claims. For a betterunderstanding of the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features are apparent from thefollowing detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1A illustrates a schematic of a process to make a tunnelingjunction (by focused electron beam cutting, focused He ion beam cuttingor other methods such as e-beam lithography/metal lift-off process) andto fine tune the junction size in accordance with an embodiment.

FIG. 1B illustrates a schematic continuing the process to make atunneling junction in accordance with an embodiment.

FIG. 1C illustrates a schematic continuing the process to make atunneling junction in accordance with an embodiment.

FIG. 2A illustrates a schematic of the integration of the tunnelingjunction with a nanopore in accordance with an embodiment.

FIG. 2B illustrates a schematic continuing the integration of thetunneling junction with the nanopore in accordance with an embodiment.

FIG. 2C illustrates a schematic continuing the integration of thetunneling junction with a nanopore in accordance with an embodiment.

FIG. 2D illustrates a schematic continuing the integration of thetunneling junction with the nanopore in accordance with an embodiment.

FIG. 2E illustrates a schematic continuing the integration of thetunneling junction with the nanopore in accordance with an embodiment.

FIG. 2F illustrates a schematic continuing the integration of thetunneling junction with the nanopore in accordance with an embodiment.

FIGS. 3A illustrates a schematic of a tunneling junction nanopore devicefor DNA sequencing in accordance with an embodiment.

FIG. 3B illustrates a schematic of the tunneling junction nanoporedevice for DNA sequencing with an organic coating in accordance with anembodiment.

FIG. 4A illustrates a schematic of the integration of a tunnelingjunction with a nanopore in accordance with an embodiment.

FIG. 4B illustrates a schematic continuing integration of the tunnelingjunction with the nanopore in accordance with an embodiment.

FIG. 4C illustrates a schematic continuing the integration of thetunneling junction with the nanopore in accordance with an embodiment.

FIG. 5 illustrates examples of molecules for self-assembly insidenanopores in accordance with an embodiment.

FIG. 6 illustrates a computer utilized according to embodiments.

FIG. 7 illustrates a flow chart according to an embodiment.

FIG. 8A illustrates a schematic to make the tunneling junction by ane-beam lithography and reactive ion etching method (as a process inFIG. 1) according to an embodiment.

FIG. 8B illustrates coating an e-beam resist on top of the layersleaving a small window according to an embodiment.

FIG. 8C illustrates etching away the visible part of the metal line inthe window according to an embodiment.

FIG. 8D illustrates removing the e-beam resist to result in thetunneling junction (shown in FIG. 1B) according to an embodiment.

FIG. 9A illustrates an e-beam lithography and metal lift-off methodwhich includes coating an e-beam resist on top of the layers and openingwindows with an enlongated extensions in between according to anembodiment.

FIG. 9B illustrates depositing a conductive (metal) layer on top of thelayer according to an embodiment.

FIG. 9C illustrates lifting off the conductive layer that is notdirectly on the substrate to result in the tunneling junction (shown inFIG. 1B) according to an embodiment.

FIG. 10A illustrates a process of electroplating deposition orelectroless deposition to shrink the initial gap according to anembodiment.

FIG. 10B illustrates the shrinking the gap by electroplating depositionor electroless deposition (shown as the tunneling junction in FIG. 1C)according to an embodiment.

FIGS. 11A, 11B, 11C, and 11D together illustrate a method of forming thetunneling junction nanopore device according to an embodiment.

DETAILED DESCRIPTION

Exemplary embodiments provide an approach to make a nanometer sizetunneling junction by focus electron beam cutting, and then to fine tunethe junction size, by expanded electron beam techniques. Exemplaryembodiments also include the integration of such tunneling junction witha nanopore for the purpose of DNA sequencing in a nanodevice.

Recently, there has been growing interest in applying nanopores assensors for rapid analysis of biomolecules such as DNA, ribonucleic acid(RNA), protein, etc. Special emphasis has been given to applications ofnanopores for DNA sequencing, as this technology is believed to hold thepromise to reduce the cost of sequencing below $1000/human genome. Oneissue in nanopore DNA sequencing is electrically differencing individualDNA bases by leveraging this nanopore platform.

In accordance with exemplary embodiments, an approach is disclosed whichuses a focused electron beam (e.g., utilizing a beam size as small as0.4 nm) to cut a thin metal layer (shown as cut line 105 in FIG. 1A) toform the tunneling junction. Under a low intensity electron beam,material migration can occur, and the material migration can be used tofine tune the gap size of the tunneling junction. If the thin metallayer is on a free-standing membrane, one can also make the nanopore(shown as nanopore 206, 208 in FIGS. 2B-2I) through the top of themembrane at the gap to create the tunneling junction right at theentrance, at the inner surface, and/or the exit of the nanopore for DNAsequencing purposes via the tunneling current.

Now turning to the figures, FIGS. 1A-1C (generally referred to asFIG. 1) illustrate a schematic of a process to make a tunneling junctionby focused electron beam cutting and to fine tune the junction size byexpanded electron beam according to an exemplary embodiment. FIGS. 1A-1Care top views of the schematic. In FIG. 1A, a substrate 101 can be anyelectrically insulating substrate, and layer 102 can be any electricallyconductive layer such as a metal on top of the substrate 101. Voltage isapplied by voltage source 103 between two ends of the conductive layer102 and current is monitored through the ammeter 104. A focused electronbeam (not shown) could be as small as 0.4 nm, and the focused electronbeam performs line scanning shown as line 105 at the center location ofconductive layer 102 (e.g., in a vacuum). One skilled in the artunderstands electron beam lithography (e-beam lithography), andunderstands the practice of scanning a beam of electrons in a patternedfashion across a surface.

The high energy, high density electron beam can sputter/etch material onits way into the vacuum gradually. When the voltage at voltage source103 is being applied, the current measured by its corresponding ammeter104 serves as a feedback that the current through ammeter 104 will dropdown to zero (0) once the conductive layer 102 is cut into two halves bythe electron beam, as shown in FIG. 1B. FIG. 1B shows a left half andright half of the conductive layer 102. In this way, one can create atunneling junction 106 without damaging the underneath substrate 101.The tunneling junction 106 which is a nanosize gap between twoelectrically conductive parts corresponds to the line 105 previouslyshown in FIG. 1A.

Note that one alternative approach to make the tunneling junction 106 isto cut the thin conductive (metal) layer 102 (shown as cut line 105 inFIG. 1A) using a focused ion beam. Similar to electron beam, high energy(1-50 keV) ions in the focused ion beam bombard the conductive (metal)layer 102 and physically mill the nanosize gap 106, as shown in FIG. 1B.The focused helium (He) ion beam can have a beam size as small as sub-nmdimensions, so gaps of sizes in the order of nanometers can be made. Ascompared to an electron beam cutting method, the focused ion beamcutting method offers a variety of ions of various masses for handlingdifferent cases. For example, He ions (as the focused ion beam) offersmall beam size (sub-nm) and deep cutting depth as small ions are easyto penetrate sold materials (i.e., the conductive layer 102). Also, Ga(gallium) ions (as the focused ion beam) offer sub-nm depth controlduring cutting as big ions have less penetration depth into solidmaterials (such as, the conductive layer 102). As a combination of Heand Ga ions in the focused ion beam method, He ions may be utilizedfirst and Ga ions may be utilized second (or vice versa) to cut thenanosize gap 106 in the conductive layer 102.

Another alternative approach to make the tunneling junction 106 (i.e.,the gap) is to use electron beam (e-beam) lithography to define/patternthe mask, and then follow up with either reactive ion etching of theconductive (metal) 102 to define the gap 106 or by a lift-off process ofthe conductive (metal) 102 to form the gap 106. Accordingly, twoexamples are shown in FIGS. 8 and 9 to make the tunneling junction 106(nanosize gap). FIG. 8 (FIGS. 8A through 8D) illustrates a schematic tomake the tunneling junction 106 (nanosize gap) by an e-beam lithographyand reactive ion etching method according to an embodiment. FIG. 8Ashows the electrically insulating substrate 101 with the electricallyconductive layer 102 on top of the substrate 101 (as discussed in FIG.1A). As shown in FIG. 8B, an e-beam resist 120, such as polymethylmethacrylate (PMMA), was coated on top of both the electricallyinsulating substrate 101 and the electrically conductive layer 102. Agap shape window 121 is made on the resist 120 by e-beam lithography.Part of the metal line 102 (of the conductive layer) is visible throughthe gap shape window 121. As shown in FIG. 8C, the visible part of metalline 102 in gap shape window 121 is etched by reactive ion etching. Asshown in FIG. 8D, the resist 120 is cleaned in a solvent (isopropylalcohol (IPA), etc.) and the metal gap 106 (i.e., tunneling junction106) is revealed. This results in the same tunneling junction 106 shownin FIG. 1B but utilizes an alternative approach. The rest of thefabrication steps are the same as described herein.

As the other example to make the tunneling junction 106 (nanosize gap),FIG. 9 (FIGS. 9A through 9C) illustrates an e-beam lithography and metallift-off method according to an embodiment.

FIG. 9A starts with the electrically insulating substrate 101, and thenan e-beam resist 122 is coated (such as polymethyl methacrylate (PMMA),etc.) on top of the electrically insulating substrate 101 (unlike FIG.1A, no conductive layer 102 is on the electrically insulating substrate101 at this point). Windows 123 and 124 are made/opened on the resist122 by e-beam lithography. Each window 123 and 124 also has anenlongated extension opened on the resist 122 with a small portion 175of resist 122 in between the enlongated extensions, and this smallportion 175 of resist 122 prevents the enlongated extensions fromconnecting (e.g., to one another) the two windows 123 and 124. The smallportion 175 may have a width of a couple of nanometers (e.g., 2, 3, 4, 5nm, and so forth) depending on the electron beam size and dose. As shownin FIG. 9B, the conductive (metal) layer 102 is deposited on top of theelectrically insulating substrate 101, the window 123 (and itsenlongated extension), and the window 124 (and its elongated extension).The conductive layer 102 covers everywhere of the chip surface. Notethat the dashed hidden lines represent the patterned two windows 123 and124 along with their respective elongated extensions hidden underneaththe conductive layer 102. Then, the chip (i.e., the conductive (metal)layer 102, the electrically insulating substrate 101, the window 123(and its enlongated extension), and the window 124 (and its elongatedextension)) is dipped in a solvent, such as IPA, which dissolves thee-beam resist 122. As such, the metal of the conductive layer 102 thathad been in contact with the e-beam resist 122 area is lifted off whilethe metal of the conductive layer 102 that had been in direct contactwith the substrate 101 remains. In this way, the conductive (metal)layer 102 with the gap 106 is made as shown in FIG. 9C. This results inthe same tunneling junction 106 shown in FIG. 1B but utilizes analternative approach. The rest of the fabrication steps are the same asdescribed herein.

Now returning back to FIG. 1, FIG. 1B further shows that with anexpanded (i.e., low intensity) electron beam covering area 107, the(metal) material in the conductive layer 102 can migrate and the gapsize of the tunneling junction 106 can be tuned; that is, the tunnelingjunction 106 can be reduced or increased in size to be the tunnelingjunction 108 shown in FIG. 1C. For example, to achieve the desired sizetunneling junction (gap) 108, a low intensity electron beam can be usedto bombard the conductive layer 102 at the tunneling junction (gap) 106(in FIG. 1B). This will cause the conductive layer 102 material to getsofter and flow under surface tension. The low intensity electron beamcan be utilized to cause the conductive layer 102 material to flow suchthat the tunneling junction (gap) 108 is widened and/or flow such thatthe tunneling junction (gap) 108 is narrowed. As seen by the decrease insize of the tunneling junction (gap) 106 in FIG. 1B to the tunnelingjunction (gap) 108 in FIG. 1C (which is not drawn to scale), materialmigration has caused the tunneling junction (gap) 106 to narrow. If thesubstrate 101 is a thin membrane, the whole tuning process can bemonitored under a transmission electron microscope in real-time. Thus,one can acquire (tune) the exact size of the tunneling junction (gap)108 by turning off the electron beam at the right moment. After finetuning the tunneling junction 106, the tunneling junction 106 is nowrepresented as the finely tuned tunneling junction (gap) 108 in FIG. 1C.

Instead of utilizing the low intensity electron beam to bombard theconductive layer 102 as discussed above, an alternative approach (FIG.10) is to utilize electrical plating of metal on the tips of the gap 106to shrink the gap 106 to be the tunneling junction 108 shown in FIG. 1C.In this case, FIG. 10 (FIGS. 10A and 10B) illustrates an example ofelectroplating or electroless deposition to shrink the tunnelingjunction 106.

As in FIGS. 1A and 1B, FIG. 10A shows the electrically insulatingsubstrate 101, the electrically conductive layer 102, the gap 106, thevoltage source 103 between two ends of the conductive layer 102, and theammeter 104 (the current increases as the resistance decreases).

FIG. 10A shows a solution 125 which may be in an open container. Thesolution 125 contains ions of metals (e.g., the same metal as theconductive layer 102) that need to be coated on the tips of the gap 106.Measured current through the ammeter 104 is utilized as an indicator ofthe size of gap 106 during electroplating. An electroplating voltagesource 126 generates the electroplating voltage for electroplating byusing electrodes 127 and 130. The electrode 127 is dipped in thesolution 127 while the electrode 130 is connected to the conductivelayer 102 (i.e., the left box not in the solution 125). The electrodepair 127 and 130 is for plating metal on the left side of gap 106.Assume that FIG. 10 is for plating of Pd (or any desired metal) on themetal gap 106 (i.e., on the tips of conducting metal 102 at the gap106). The solvent 125 for electroplating of Pd can be PdCl₂, Pd acetate,and/or Pd(NH₃)₂Cl₂. Voltage of the voltage source 126 is turned on toplace a thin layer of the ions of metal (such as Pd ions) onto (e.g.,the left tip of) the gap 106 to reduce its size to the tunnel junction108 shown in FIG. 10B. Once the desired gap size is achieved (indicatedfrom increased current measured on ammeter 104), the plating process canbe stopped by turning off the voltage source 126. The final gap 108 isshown as tunneling junction 108 in FIG. 10B.

In the case of electroless deposition, the electrodes 126 and 127 willnot be needed, but a reducing agent (i.e., in the solution 125) isneeded to react with metal salt to produce metal on the tips of (theconducting metal 102 at) the gap 106. For electroless deposition of Pdon the gap 106, the solution 125 may be Pd(NH₃)₂Cl₂ with the reducingagent being a mixture of NH₄OH, Na₂EDTA (EDTA isethylenediaminetetraacetic acid), and/or Hydrazine at temperature of 80C. Once the desired gap size is achieved (as indicated from the increasein current measured by ammeter 104), the plating process can be stoppedby removing the solution 125 for electroless deposition. Again, thefinal (narrowed) gap is shown as tunneling junction 108 in FIG. 10B. Therest of the fabrication steps for making the completed device are thesame as described herein.

FIGS. 2A-2F illustrate a schematic of the integration of the tunnelingjunction 108 with a nanopore in accordance with an exemplary embodiment.FIGS. 2A, 2B, 2D, and 2E (including 4A and 4B) are a cross-sectionalview of the schematic, and FIGS. 2C and 2F (including 4C) are top viewsof the schematic. In FIG. 2A, the substrate 201 can be any substrate,such as Si (silicon). Layers 202 and 203 are electrically insulatingfilms, such as Si₃N₄ (compound of silicon and nitrogen). The insulatinglayer 203 serves as an etching mask for etching thorough the substrate201 via either dry or wet etching, and the etching stops on insulatinglayer 202. In this way, part of the insulating layer 202 will be afree-standing membrane. Conductive layer 204 (corresponding toconductive layer 102 in FIG. 1) is an electrically conductive layer, andtunneling junction 205 (corresponding to tunneling junction/gap 108 inFIG. 1) is the tunneling junction made in the free-standing membranepart of conductive layer 204 using the method described in FIG. 1. Thetunneling junction 205 will be visible under a transmission electronmicroscope, and a nanometer size pore (nanopore) 206 can be made throughthe tunneling junction 205 and the underneath insulating layer 202, asshown in FIG. 2B. In this way, the tunneling junction 205 is integratedwith the nanopore 206. As seen in FIG. 2B, the nanopore 206 is a holethrough the insulating layer 202 while the tunneling junction 205 is agap in the conductive layer (metal) 204.

FIG. 2C shows a top view of the schematic in FIG. 2B. As seen in the topview of FIG. 2C, the tunneling junction 205 (corresponding to tunnelingjunction/gap 108 in FIG. 1) is only between the conductive layer (metal)204 (corresponding to conductive layer 102), and the tunneling junction205 splits the conductive layer 204 into a left half and a right half.The nanopore 206 is formed through the tunneling junction 205 and goesthrough the substrate 201.

In order to work with an electrically conductive solution, an insulating(cap) layer 207 (also called the passivation layer which may be a layerof oxide and/or silicon nitride) is deposited on the conductive layer204, as shown in FIG. 2D (e.g., right after the tunneling junction 205is made). The tunneling junction 205 will be visible under atransmission electron microscope and a nanometer size pore (nanopore)208 can be made through the tunneling junction 205 and the underneathinsulating layer 202, as shown in FIG. 2E. In this way, the tunnelingjunction 205 is embedded in the nanopore 208. The nanopore 206 may nowbe considered part of the nanopore 208. Via windows 209 and 210 areopened through the insulating layer 207 down to the conductive layer204, for electrically accessing the two sides of the tunneling junction205. The windows 209 and 210 will be used as electrodes/connections forconnecting, e.g., a wire to the left and right halves of the conductivelayer 204.

FIG. 2F illustrates the top view of FIG. 2E. In FIG. 2F, the conductivelayer 204 (shown as an outline with a dotted line) is buried underneaththe insulation (passivation) layer 207 with windows 209 and 210 of theconductive layer 204 exposed. Although not visible in FIG. 2F, thenanopore 208 goes through the insulating layer 202 and the insulation(passivation) layer 207.

FIGS. 4A, 4B, and 4C illustrate a variation of FIGS. 2A-2F in which thenanopore 208 and tunneling junction are made in the same electron beamcutting process and have the same shape in accordance with an exemplaryembodiment. An insulating (cap) layer 207 (also called the passivationlayer which may be a layer of oxide and/or silicon nitride) is depositedon the conductive layer 204, as shown in FIG. 4A. A focused electronbeam is used to cut through all layers 207, 204, and 202 at thefreestanding membrane part and to cut conductive layer 204 into twohalves, as shown in FIG. 4B. In this way, the tunneling junction 205 andthe nanopore 208 have exactly the same shape. Via windows 209 and 210are opened through the insulating layer 207 down to the conductive layer204, for electrically accessing the two sides of the tunneling junction205. The windows 209 and 210 will be used as electrodes/connections forconnecting, e.g., a wire to the left and right halves of the conductivelayer 204.

FIG. 4C illustrates the top view of FIG. 4B. In FIG. 4C, the conductivelayer 204 (shown as a dotted line) is buried underneath the insulating(passivation) layer 207 with windows 209 and 210 of the conductive layer204 exposed. Although not visible in FIG. 4C, the nanopore 208 goesthrough the insulating layer 202 and the insulating (passivation) layer207.

FIGS. 3A and 3B illustrate a schematic (system) of a tunneling junction(e.g., tunneling junction 106, 108, and 205) and nanopore device 300 forDNA sequencing according to an exemplary embodiment. FIGS. 3A and 3Bshow a cross-sectional view of the tunneling junction and nanoporedevice 300.

In FIGS. 3A and 3B, elements 301-310 are the same as elements 201-210respectively. However, FIG. 3B includes an organic coating as discussedherein. The tunneling junction and nanopore device 300 partitions tworeservoirs 311 and 312. Electrically conductive solution 313 fills thetwo reservoirs 311 and 312 as well as the nanopore 308. A negativelycharged DNA 314 (with each base illustrated as base 315) can be driveninto the nanopore 308 by a voltage of the voltage source 318 appliedbetween the two reservoirs 311 and 312 via two electrodes 316 and 317,respectively. Voltage of the voltage source 319 is applied between thetwo sides (at left window 309 and right window 310) of the tunnelingjunction 305, and a baseline tunneling current is monitored at ammeter320. The baseline tunneling current may be stored in memory 15 of acomputer 600 (shown in FIG. 6) for further use as discussed herein. AsDNA bases 315 pass through the tunneling junction 305 (which is the gapin the conductive (metal) layer 304), each of the DNA bases 315 can beindentified by its respective tunneling current signal at the ammeter320.

For example, voltage source 318 is turned on to drive the DNA 314 intothe tunneling junction 305 which is the gap separating the conductivelayer 304 into two halves. When, e.g., a base 315 a is in the tunnelingjunction 305, voltage source 319 is turned on (while voltage source 318is turned off) to measure the tunneling current of the base 315 a. Forinstance, with voltage applied by voltage source 319, current flowsthrough window 309 (acting as an electrode) of conductive layer 304,through the conductive layer 304, into the conductive solution (liquid)313, into the DNA base 315 a (which produces the tunneling currentsignature), out through the conductive solution 313, into the right sideof the conductive layer 304, out through the window 310 (acting as anelectrode), and into the ammeter 320 for measurement. The ammeter 320may be implemented by and/or integrated in the computer 600 (testequipment) for measuring the baseline tunneling current and tunnelingcurrent generated by the DNA base 315 a. A software application 605 ofthe computer 600 is configured to measure, display, plot/graph, analyze,and/or record the measured tunneling current for each DNA base 315 thatis tested. In the example above, the software application 605 (and/or auser utilizing the software application 605) can compare the baselinetunneling current measured with no DNA base 315 in the tunnelingjunction 305 to the tunneling current corresponding to each DNA base 315(at a time) that is measured in tunneling junction 305. In the example,the tunneling current (signal) for the DNA base 315 a is comparedagainst the baseline tunneling current by the software application 605(or a user utilizing the software application 605). The tunnelingcurrent (signature) for the DNA base 315 a may have particularcharacteristics that are different from the baseline tunneling currentmeasured by the ammeter 320, and the tunneling current (signatures) forthe DNA base 315 a can be utilized to identify and/or differentiate theDNA base 315 a from other DNA bases 315 on the DNA 314.

For example, the measured tunneling current signature for DNA base 315 amay have a positive pulse, a negative pulse, a higher or lower current(magnitude), an inverse relationship, a rising or falling plot, aparticular frequency, and/or any other difference from the baselinetunneling current that can be determined by the software application 605(and/or a user viewing the display 45 of the two different plots). Thisunique tunneling current signature can be utilized (by the softwareapplication 605) to distinguish the DNA base 315 a from other DNA bases315. Note that the tunneling current measured at ammeter 320 betweenelectrode layers does not require any electrical wiring between the leftand right parts (which will be shown as electrodes 304 a and 304 b inFIG. 3B) of the conductive (electrode) layers 304 as electrons simplymove from one electrode to the other in a quantum mechanical way. Forexample, there will be a baseline tunneling current when DNA base 315 ais away (e.g., with distance much longer than the wavelength of anelectron) from the tunneling junction 305. When DNA base 315 a is close(e.g., within the distance of the wavelength of an electron) to thetunneling junction 305, the tunneling path of the electron will bererouted to tunnel from the left part of the conductive (electrode)layer 304 to the DNA base 315 a and then to the right part of theconductive (electrode) layer 304. In this way, the tunneling current(electrons) through the DNA base 315 a will create a current signature(such as an increase of tunneling current, typically in the order oftens of pA (picoamperes)) added onto the baseline tunneling currenttrace. The tunneling current across DNA bases is dependent on theelectronic and chemical structure of the DNA bases; thus, a differentDNA base will generate a different tunneling current signature. If thedifference between the tunneling current signatures of different basesis small or stochastic, repeating measurements on the same DNA base canbe done; a histogram of the amplitudes of the tunneling currentsignatures can be fit and the statistical data will provide enoughresolution to differentiate DNA bases.

FIG. 3B utilizes the approach discussed for FIG. 3A except that theconductive layer 304 is coated with organic coating 325, which can formtransient bonds 321 (such as a hydrogen bond (i.e., transient bonds 321)with the DNA base 315). In FIG. 3B, these transient bonds 321 formed bythe organic coating 325 will fix the orientation of the DNA base 315 andthe relative distance of the DNA base 315 to the conductive layer 304,for improving the tunneling current signal measured by ammeter 320 andfor better indentifying DNA bases 315. If the organic coating 325 and/ortransient bonds 321 are electrically conductive, they will help toshrink the tunneling gap size and enhance the tunneling currentsignatures too. Also, the transient bonds 321 by the organic coating 325hold the DNA 314 in place against thermal motion when measuring thetunneling current of the base 315. The forces of thermal motion maycause the DNA 314 to move, but the transient bonds 321 fix the base 315in the tunneling junction 305 against the DNA movement caused by thermalmotion.

In one implementation, the organic coating 325 consists of bifunctionalsmall molecules which at one end form covalent bonds with conductivelayer 304, and at the other end (of the organic coating 325) which isexposed in the nanopore 308, the organic coating 325 consists offunctionalities which can form strong hydrogen bonds with DNA and/or canprotonate nucleotides to form acid base interactions. If the conductivelayer 304 is made of metals such as gold, palladium, platinum etc., thefirst functionality which bonds to the conductive layer 304 can bechosen as thiols, isocyanides, and/or diazonium salts. If the conductivelayer 304 is made of titanium nitrides or indium tin oxide (ITO), thecovalent bonding functionality is chosen from phosphonic acid,hydroxamic acid, and/or resorcinol functionality. The small bifunctionalmolecules are designed in such a way that any charge formation due tointeraction with DNA can easily be transferred to the conductive layer304 and therefore a pi-conjugated moiety (e.g., benzene, diphenyl, etc.)are sandwiched between two functionalities. The second functionality isa group which can form a strong hydrogen bond with DNA. Examples of suchgroups include but are not limited to alcohols, carboxylic acids,carboxamides, sulfonamides, and/or sulfonic acids. Other groups whichcan be used to form interactions with DNA are individual self-assemblednucleotides. For example, adenine monophosphonic acid, guaninemonophosphonic acid, etc., can be self-assembled on titanium nitrideelectrodes or mercapto thymine or mercapto cytosine self-assembles onmetal electrodes such as gold and/or platinum. FIG. 5 illustratesexamples of molecules for self-assembly inside nanopores according toexemplary embodiments. The molecules may be utilized as the organiccoating 325.

Referring to FIG. 3B, as discussed above, the voltage source 318 isapplied to move the DNA 314 into the nanopore 308. When voltage of thevoltage source 319 is applied (and the voltage source 318 is turnedoff), current flows through left electrode 304 a, into the organiccoating 325 a, into the transient bond 321 a (which acts as or can bethought of as a wire), into the DNA base 315 a (producing the tunnelingcurrent), out through the transient bond 321 b, out through the organiccoating 325 b, out through the right electrode 304 b, and into theammeter 320 to measure the tunneling current of the DNA base 315 a. Theammeter 320 may be integrated with the computer 600, and the computer600 can display on display 45 the tunneling current of the DNA base 315a versus the baseline tunneling current measured when no base 315 is inthe tunneling junction 305.

FIG. 7 illustrates a method 700 forming the tunneling junction nanoporedevice 300 according to exemplary embodiments, and reference can be madeto FIGS. 1, 2, and 3.

At operation 705, a tunneling junction 108, 205, 305 is made by electronbeam sculpting (cutting or size-tuning). Using a low intensity electronbeam, the tunneling junction 108, 205, 305 can be widened by causing thematerial (metal) of the conductive layer 102, 204, 304 to migrate awayfrom the tunneling junction gap, thus making the gap wider; similarly,using a low intensity electron beam spread across area 107 in FIG. 1,the tunneling junction 108, 205, 305 can be narrowed to cause thematerial of the conductive layer 102, 204, 304 to flow toward (into) thetunneling junction gap thus make the gap smaller.

At operation 710, the tunneling junction 108, 205 is integrated with ananopore 208 as shown in FIGS. 2B-2F. The integrated (combined)tunneling junction 205 and nanopore 208 form a hole through multiplelayers 207, 204, and 202 as shown in FIG. 2E. The distinction betweenthe tunneling junction 205 and the nanopore 208 can be seen in FIG. 2F.This distinction is carried through to the tunneling junction 305 shownin FIG. 3 in which the tunneling junction 305 is the gap between theconductive layer 304 (i.e., separating the conductive layer 304 into twohalves) but not layers 307, 302, 301, and 303. In one implementation,the tunneling junction 108, 205 is formed prior to forming the nanopore208 (and/or nanopore 206).

At operation 715, the nanopore 208 partitions two conductive ionicbuffer reservoirs 312 and 313, and the DNA 314 is electrically loadedinto the nanopore 308 and the tunneling junction 305. The tunnelingjunction 305 is between the left half 304 a and right half 304 b of theconductive layer 304. The left and right halves 304 a and 304 b serve aselectrodes for accessing the tunneling junction 305 (and the base 315therein) by the voltage source 319 to measure the tunneling current withammeter 320.

At operation 720, the DNA bases 315 are differentiated using thetunneling current of each individual base 315 (measured by ammeter 320)with and/or without organic coating 325 on the inside surface of thetunneling junction 305. The computer 600 can measure, analyze,differentiate, display, and record/store (in memory 15) the differenttunneling currents measured for the different bases 315 of the DNA 314.The tunneling current measurements of the bases 315 with the organiccoating 325 causing the transient bonds 321 a and 321 b would bedifferent from the tunneling currents measurements of the same bases 315without the organic coating 325 and without the transient bonds. Forexample, the tunneling current measured for base 315 a with the organiccoating 325 (causing transient bonds 321 a and 321 b) may have a greatermagnitude than without the organic coating 325.

Turning to FIGS. 11A, 11B, 11C, and 11D (generally referred to as FIG.11), FIG. 11 is a method 1100 of forming the nanodevice 300 discussedherein. The reservoir is filed with the conductive fluid 313 at block1102. A membrane is formed to separate the reservoirs 311 and 312 in thenanodevice 300, where the membrane includes an electrode layer 102having a tunneling junction (gap 106) formed therein at block 1104. Themembrane has the nanopore 206 formed through other layers of themembrane such that the nanopore 206 is aligned with the tunnelingjunction of the electrode layer at block 1106.

The tunneling junction 106 of the electrode layer 102 is narrowed to anarrowed size (i.e., to the size of the tunneling junction 108) byelectroplating or electroless at block 1108. Options for forming thetunneling junction 106 before being narrowed to the tunneling junction108 are discussed below.

With reference to FIG. 11B, as one option, the tunneling junction isformed in the electrode layer 102 by: initially forming the electrodelayer 102 with two boxes connected by a metal strip of the electrodelayer at block 1124 (as shown in FIG. 8A), coating an electron beamresist 120 on top of the electrode layer 102 at block 1126 (as shown inFIG. 8B), opening a gap shaped window 121 through the electron beamresist 120 to make a portion (102) of the metal strip visible throughthe gap shaped window 121 of the electron beam resist 120 at block 1128,etching away the portion of the metal strip that was visible through thegap shaped window 121 of the electron beam resist 120 at block 1130 (asshown in FIG. 8C), and removing the electron beam resist 120 resultingin the electrode layer 102 having the tunneling junction 106 where theportion of the metal strip was etched away at block 1132 (as shown inFIG. 8D).

Reactive ion etching may be used to etch away the portion of the metalstrip that was visible through the gap shaped window 121 of the electronbeam resist 120. As such, the electrode layer 102 underneath theelectron beam resist 120 remains and is not etched away. The electronbeam resist is polymethyl methacrylate (PMMA). Electron beam lithographmay be utilized to open the gap shaped window 121 through the electronbeam resist 120 to make the portion of the metal strip visible throughthe gap shaped window of the electron beam resist 120.

With reference to FIG. 11C, as another option, the tunneling junction(i.e., the gap 106) is formed in the electrode layer 102 by: coating anelectron beam resist 122 on top of a substrate 101 at block 1134,opening a first window 123 having a first elongated extension in thecoated electron beam resist at block 1136 (as shown in FIG. 9A), andopening a second window 124 having a second elongated extension in whicha portion 175 of the electron beam resist 122 separates the firstelongated extension from the second elongated extension at block 1138(as shown in FIG. 9A). Additionally, metal of the electrode layer 102 isdeposited to cover the electron beam resist, to cover the first windowhaving the first elongated extension, and to cover the second windowhaving the second elongated extension at block 1140 (as shown in FIG.9B). The metal that was contact with the electron beam resist 122 isremoved so as to leave the electrode layer 102 having the tunnelingjunction 106 in a pattern of the first window 123 (along with its firstelongated extension) and in the pattern of the second window 124 (alongwith its second elongated extension), where the tunneling junction 106is formed and located where the portion 175 of the electron beam resist122 was removed from at block 1142 (as shown in FIG. 9C).

With reference to FIG. 11D, as one option, narrowing the tunnelingjunction of the electrode layer 102 to the narrowed size is byelectroplating which includes: placing the tunneling junction 106 in asolution 125 having metal ions of a metal at block 1110, applying anelectroplating voltage (via voltage source 126) to one end of theelectrode layer 102 not in the solution 125 and to another end of theelectrode layer 102 having the tunneling junction 106 in the solution125 at block 1112 (as shown in FIG. 10A), and causing the metal ions ofthe metal to narrow the tunneling junction 106 to the narrowed size byattaching to tips of the tunneling junction at block 1114 (as shown inFIG. 10B). The electroplating voltage is turned off when the narrowedsize of the tunneling junction 108 is achieved. For electroplating withPd, the solution includes at least one of PdCl₂, Pd acetate, andPd(NH₃)₂Cl₂.

As another option in FIG. 11D, narrowing the tunneling junction of theelectrode layer to the narrowed size is by electroless which includes:placing the tunneling junction 106 in a solution 126, in which thesolution 125 includes metals ions of metal at block 1116, and combiningthe solution 125 of the metal ions with a chemical reducing agent (nowadded to the solution 125) to react with the metal ions, which causesthe metal ions of the metal to narrow the tunneling junction to thenarrowed size by attaching to tips of the tunneling junction at block1118 (as shown in FIG. 10B). The tunneling junction 108 is removed fromthe solution 125 once the narrowed size of the tunneling junction isachieved. For electroless deposition of Pd, the solution of the metalions is Pd(NH₃)₂Cl₂, and the chemical reducing agent includes a mixtureof NH₄OH, Na₂EDTA, and/or Hydrazine at a temperature of 80 Celsius.

When a voltage is applied to the electrode layer, a tunneling current isgenerated by a base in the tunneling junction to be measured as acurrent signature for distinguishing the base at block 1120. When anorganic coating is applied on an inside surface of the tunnelingjunction, transient bonds are formed between the electrode layer and thebase at block 1122.

The material of the electrode layer includes at least one of gold,palladium, platinum, titanium nitride, ruthenium, dope zinc oxide,indium tin oxide, tungsten, aluminum, and copper. In one case, thetunneling junction 106 is cut into the electrode layer 102 by a focusedelectron beam and/or by an He ion beam.

Now turning to FIG. 6, FIG. 6 illustrates a block diagram of thecomputer 600 having various software and hardware elements forimplementing exemplary embodiments. The computer 600 may be utilized inconjunction with any elements discussed herein.

The diagram depicts the computer 600 which may be any type of computingdevice and/or test equipment (including ammeters, voltage sources,connectors, etc.). The computer 600 may include and/or be coupled tomemory 15, a communication interface 40, display 45, user interfaces 50,processors 60, and software 605. The communication interface 40comprises hardware and software for communicating over a network andconnecting (via cables, plugs, wires, electrodes, etc.) to thenanodevices discussed herein. Also, the communication interface 40comprises hardware and software for communicating with, operativelyconnecting to, reading, and controlling voltage sources, ammeters,tunneling currents, etc., as discussed herein. The user interfaces 50may include, e.g., a track ball, mouse, pointing device, keyboard, touchscreen, etc, for interacting with the computer 600, such as inputtinginformation, making selections, independently controlling differentvoltages sources, and/or displaying, viewing and recording tunnelingcurrent signatures for each base, etc.

The computer 600 includes memory 15 which may be a computer readablestorage medium. One or more applications such as the softwareapplication 605 (e.g., a software tool) may reside on or be coupled tothe memory 15, and the software application 605 comprises logic andsoftware components to operate and function in accordance with exemplaryembodiments in the form of computer executable instructions. Thesoftware application 605 may include a graphical user interface (GUI)which the user can view and interact with according to exemplaryembodiments.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneore more other features, integers, steps, operations, elementcomponents, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

While the exemplary embodiments of the invention have been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

1-20. (canceled)
 21. A nanodevice comprising: a reservoir filled with aconductive fluid; and a membrane formed to separate the reservoir in thenanodevice, the membrane including an electrode layer having a tunnelingjunction formed therein; wherein the membrane is formed to have ananopore formed through one or more other layers of the membrane suchthat the nanopore is aligned with the tunneling junction of theelectrode layer; wherein the tunneling junction of the electrode layeris narrowed to a narrowed size by electroplating or electrolessdeposition; wherein when a voltage is applied to the electrode layer, atunneling current is generated by a base in the tunneling junction to bemeasured as a current signature for distinguishing the base; and whereinwhen an organic coating is formed on an inside surface of the tunnelingjunction, transient bonds are formed between the electrode layer and thebase.
 22. The nanodevice of claim 21, wherein narrowing the tunnelingjunction of the electrode layer to the narrowed size by theelectroplating includes: placing the tunneling junction in a solutionhaving metal ions of a metal; applying an electroplating voltage to oneend of the electrode layer not in the solution and to another end of theelectrode layer having the tunneling junction in the solution; andcausing the metal ions of the metal to narrow the tunneling junction tothe narrowed size by attaching to tips of the tunneling junction. 23.The nanodevice of claim 22, wherein the electroplating voltage is turnedoff when the narrowed size of the tunneling junction is achieved. 24.The nanodevice of claim 22, wherein for electroplating with Pd, thesolution includes at least one of PdCl₂, Pd acetate, and Pd(NH₃)₂Cl₂.25. The nanodevice of claim 21, wherein narrowing the tunneling junctionof the electrode layer to the narrowed size by the electroless includes:placing the tunneling junction in a solution, the solution includingmetals ions of metal; and combining the solution of the metal ions witha chemical reducing agent to react with the metal ions, which causes themetal ions of the metal to narrow the tunneling junction to the narrowedsize by attaching to tips of the tunneling junction.
 26. The nanodeviceof claim 25, wherein the tunneling junction is removed from the solutiononce the narrowed size of the tunneling junction is achieved.